1. Field of the Invention
The present invention relates to a process for preparing improved inorganic pigment having enhanced dispersibility in paints and plastics concentrates as determined by the time or energy required to achieve dispersal.
2. Description of the Prior Art
Inorganic pigments such as titanium dioxide, zinc sulfide, zinc oxide and the like are used in paint, plastics and other products. Such pigments have heretofore been difficult to disperse in paints and plastics concentrates, i.e., the pigments have required long time periods and/or high levels of energy to achieve dispersal. Inorganic pigments are generally in the form of a finely divided powder which has been jet-milled or micronized as a final step in their production.
More recently, processes have been developed and used for preparing low-dusting, free-flowing pigment which requires less energy to disperse in paints and plastics concentrates. For example, U.S. Pat. No. 5,733,365 issued to Halko et al. on Mar. 31, 1998 and its related U.S. Pat. No. 5,908,498 issued to Kauffman et al. on Jun. 1, 1999 disclose a process for preparing improved low-dusting, free-flowing pigments which have not been subjected to final micronizing treatments. The process is comprised of the steps of providing an inorganic pigment material which has not been micronized, providing a source of water, forming a fine, well dispersed slurry of the pigment and water, milling the slurry, adjusting the pH of the slurry, depositing a treating agent having the formula ROOCCHSO3MCH2COORxe2x80x2 wherein R and Rxe2x80x2 are monovalent alkyl radicals having from about 2 to about 20 carbon atoms and M is a metallic monovalent cation on the slurried milled pigment, and then drying the pigment material having the treating agent deposited thereon. The presence of the treating agent makes the pigment produced more readily dispersible in paints and plastics concentrates.
While the pigments produced in accordance with the teachings of the above described patents constitute a major improvement as compared to prior pigments, the dispersal of the pigments in paints and plastics concentrates still requires considerable mixing time, energy and expense.
Thus, there is a continuing need for a process for preparing improved pigments which are more easily dispersed in paints and plastics concentrates.
The present invention provides a process for preparing improved pigment which is more readily dispersible in paints and plastics concentrates, and therefore, meets the need described above and overcomes the deficiencies of the prior art. The process of this invention basically comprises the steps of: (a) mixing a particulate pigment with water to form a slurry of the pigment and water; (b) mixing a surface active agent with the slurry of step (a) so that the pigment is coated therewith, the surface active agent being selected from the group consisting of alkyl alcohols ethoxylated with from about 4 to about 14 ethylene oxide groups and wherein the alkyl groups have from about 6 to about 16 carbons atoms, ethoxylated sorbitan derivatives having HLB values in the range of from 1 to about 20, a mixture of non ethoxylated mono and diglycerides and ethoxylated mono and diglycerides having HLB values in the range of from 1 to about 20 and mixtures of said ethoxylated sorbitan derivatives, said non-ethoxylated mono and diglycerides and said ethoxylated mono and diglycerides; and (c) drying the pigment coated in accordance with step (b).
Another process of this invention for preparing improved pigment which is highly dispersible in paints and plastics concentrates comprises the steps of: (a) mixing a particulate pigment with water to form a slurry of the pigment and water; (b) milling the slurry formed in step (a) to produce a pigment particle size in the range of from about 0.1 micron to about 1 micron; (c) mixing a surface active agent with the slurry of step (b) so that said pigment is coated therewith, said surface active agent being selected from the group described above; and (d) drying the pigment coated in accordance with step (c).
It is, therefore, a general object of the present invention to provide a process for preparing improved pigments which are more readily dispersible in paints and plastics concentrates.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows.
As mentioned, it has heretofore been difficult to disperse particulate pigment in paints and plastics concentrates or melts. The pigments utilized in paints and plastics concentrates include, but are not limited to, white opacifying pigments such as titanium dioxide, basic carbonate white lead, basic sulfate white lead, basic silicate white lead, zinc sulfide, zinc oxide, composite pigments of zinc sulfide and barium sulfate, antimony oxide and the like, white extender pigments such as calcium carbonate, calcium sulfate, china and kaolin clays, mica, diatomaceous earth and colored pigments such as iron oxide, lead oxide, cadmium sulfide, cadmium selenide, lead chromate, zinc chromate, nickel titanate, chromium oxide and the like. Of the foregoing pigments, inorganic pigments are preferred with titanium dioxide being the most preferred.
The pigments produced by the present invention are more readily dispersed in paints and plastics concentrates and require less time and/or energy to disperse than prior art pigments. The treated pigments produced by this invention can be low-dusting and free-flowing non-micronized pigments or the treated pigments can optionally be micronized.
The process of the present invention for preparing improved pigment which is more readily dispersible in paints and plastics concentrates is basically comprised of the following steps: (a) mixing a particulate pigment with water to form a slurry of the pigment and water; (b) mixing a surface active agent with the slurry of step (a) so that the pigment is coated therewith; and (c) drying the pigment coated in accordance with step (b).
The particulate pigment utilized in step (a) of the above process is preferably pigment which has not been milled or micronized. The preferred non-treated titanium dioxide pigment for use in the process of this invention can be of either the anatase or rutile crystalline structure or a combination thereof. The titanium dioxide pigment can be produced by a commercial process which is well known to those skilled in the art such as the sulfate process or the vapor phase chloride oxidation process.
The surface active agents which can be utilized in accordance with the present invention include alkyl alcohols ethoxylated with from about 4 to about 14 ethylene oxide groups and wherein the alkyl groups have from about 6 to about 16 carbon atoms, ethoxylated sorbitan derivatives having hydrophile-lipophile balances (HLB values) in the range of from about 1 to about 20, a mixture of non-ethoxylated mono and diglycerides and ethoxylated mono and diglycerides having HLB values in the range of from about 1 to about 20 and mixtures of said ethoxylated sorbitan derivatives, said non-ethoxylated mono and diglycerides and said ethoxylated mono and diglycerides.
Of the foregoing surface active agents, a mixture of ethoxylated sorbitan derivatives having HLB values in the range of from about 2 to about 15, non-ethoxylated mono and diglycerides having HLB values in the range of from about 2 to about 15 and ethoxylated mono and diglycerides having HLB values in the range of from about 2 to about 15 is preferred. The ethoxylated sorbitan derivatives are preferably present in the mixture in an amount in the range of from about 5% to about 100% by weight of the mixture with the non-ethoxylated mono and diglycerides and ethoxylated mono and diglycerides making up the remainder of the mixture. A more preferred mixture of the ethoxylated sorbitan derivatives, non-ethoxylated mono and diglycerides and ethoxylated mono and diglycerides contain the ethoxylated sorbitan derivatives in an amount in the range of from about 15% to about 70% by weight of the mixture with the non-ethoxylated and ethoxylated mono and diglycerides making up the remainder of the mixture. Most preferably, the surface active agent mixture contains the ethoxylated sorbitan derivatives in an amount of about 70% with non-ethoxylated and ethoxylated mono and diglycerides making up the remaining 30% by weight of the mixture.
An example of a suitable commercially available ethoxylated sorbitan derivative which can be utilized in accordance with this invention is an ethoxylated sorbitan monooleate sold by BASF Corporation under the trade designation xe2x80x9cT-MAZ-81(trademark).xe2x80x9d An example of a suitable commercially available mixture of non-ethoxylated mono and diglycerides and ethoxylated mono and diglycerides which can be utilized is sold by Loders Croklaah Company under the trade designation xe2x80x9cTally 100 Plus(trademark).xe2x80x9d
The slurry formed in step (a) described above generally contains pigment in an amount in the range of from about 10% to about 50% by weight of the slurry, preferably an amount in the range of from about 20% to about 40% and most preferably about 34%. The slurry is generally formed in accordance with step (a) at a temperature in the range of from about 10xc2x0 C. to about 90xc2x0 C., preferably from about 15xc2x0 C. to about 80xc2x0 C. and most preferably at a temperature of about 25xc2x0 C.
The pH of the slurry formed in step (a) is adjusted, if necessary, to a pH in the general range of from about 7.0 to about 13.0, more preferably a pH of from about 8.0 to about 11.0 and most preferably about 9.5. Also, the slurry can optionally be filtered to increase the pigment content of the slurry to in the range of from about 40% to about 95% solids prior to carrying out step (b).
The process of the present invention can also optionally include the step of coating the pigment with a metal oxide while the pigment is in the slurry formed in step (a). Examples of metal oxides which can be used include, but are not limited to, aluminum oxide, silica and zirconium oxide. Preferably, the coating of the pigment with a metal oxide yields a coating of from about 0.25% to about 1.5% metal oxide by weight of pigment. Such coatings improve the pigmentary properties of the pigment product and are well known to those skilled in the art.
The surface active agent utilized is generally mixed with the slurry in accordance with step (b) in an amount in the range of from about 0.1% to about 5.0% by weight of pigment in the slurry, preferably in an amount in the range of from about 0.25% to about 2.0% and most preferably in an amount of 1.0%. The mixing of the surface active agent with the slurry in accordance with step (b) is generally carried out in a time period in the range of from about 5 minutes to about 24 hours, preferably in a time period from about 5 minutes to about 30 minutes and most preferably in a time period of about 5 minutes.
The surface active agent is generally coated on the pigment in accordance with step (b) in an amount in the range of from about 0.1% to about 5% by weight of the pigment, preferably in an amount of from about 0.5% to about 2% by weight of the pigment and most preferably in an amount of about 1%.
The drying of the surface active agent coated pigment in accordance with step (c) is preferably carried out by spray drying the pigment. However, as will be understood by those skilled in the art, other drying equipment can be utilized such as an agglomerator, a fluid bed dryer or the like. As mentioned above, if desired, the dried coated pigment can be micronized.
A preferred process of the present invention for preparing an improved titanium dioxide pigment which is more readily dispersible in paints and plastics concentrates than prior art pigments comprises the following steps: (a) mixing a particulate titanium dioxide pigment with water to form a slurry of the pigment and water; (b) mixing a surface active agent with the slurry of step (a) so that the pigment is coated therewith, the surface active agent being a mixture of ethoxylated sorbitan derivatives having HLB values in the range of from about 2 to about 15, nonethoxylated mono and diglycerides having HLB values in the range of from about 2 to about 15 and ethoxylated mono and diglycerides having HLB values in the range of from about 2 to about 15; and (c) spray drying the titanium dioxide pigment coated in accordance with step (b).
The ethoxylated sorbitan derivative in the mixture of surface active agents is preferably present therein in an amount of about 70% by weight of the mixture with the non-ethoxylated mono and diglycerides and ethoxylated mono and diglycerides making up the remainder of the mixture. Also, the pigment is preferably present in the slurry formed in step (a) in an amount of about 34% by weight of the slurry and the slurry is preferably formed at a temperature of about 25xc2x0 C. The surface active agent mixture is mixed with the slurry in accordance with step (b) in an amount of about 1% by weight of pigment in the slurry, and the surface active agent is preferably coated on the pigment in accordance with step (b) in an amount of about 1% by weight of the pigment. Step (c) is preferably carried out in a time period of about 5 minutes. When the pigment is coated with a metal oxide during step (a), if necessary, the pH of the slurry can be adjusted to in the range of from about 8 to about 11. Also, as mentioned above, the slurry can be filtered to increase the concentration of pigment in the slurry prior to carrying out step (b).
Another process of this invention for preparing improved pigment which is more readily dispersible in paints and plastics concentrates is basically comprised of the following steps: (a) mixing a non-micronized particulate pigment with water to form a slurry of the pigment and water; (b) milling the slurry formed in step (a) to produce a pigment particle size therein in the range of from about 0.1 micron to about 1 micron; (c) mixing a surface active agent with the slurry of step (b) so that the pigment is coated therewith; and (d) drying the pigment coated in accordance with step (c). As mentioned, the dried pigment can be micronized if desired.
The surface active agents which can be utilized in the immediately preceding process for preparing pigment are the same as those described above. Also, the slurry formed in step (a) contains pigment in the amounts set forth above and has a temperature in the range described above.
The milling of the slurry in step (b) is carried out to produce a pigment particle size in the slurry in the range of form about 0.1 micron to about 1 micron, preferably a size in the range of from about 0.1 micron to about 0.8 micron and most preferably about 0.2 micron. While a variety of milling apparatus can be utilized, a sand mill is preferred.
After the slurry is milled, and as mentioned above, the pH of the slurry can be adjusted to the levels described above and can be filtered as described above. Further, the pigment in the milled slurry can be coated with a metal oxide in the amounts described above.
The surface active agent utilized is generally mixed with the slurry in accordance with step (c) in the amounts given above, the mixing of the surface active agent with the slurry is carried out in the time mentioned above and the surface active agent is coated on the pigment in the amounts given above. Finally, the drying of the surface active agent coated pigment in accordance with step (d) is preferably carried out by spray drying the pigment but other drying equipment can be utilized. If the dried product produced in step (d) is subsequently micronized, a jet mill is preferably utilized.
A preferred process of the present invention for preparing an improved titanium dioxide pigment which is dispersible in paints and plastics concentrates comprises the following steps: (a) mixing a non-micronized particulate titanium dioxide pigment with water to form a slurry of the pigment and water; (b) milling the slurry formed in step (a) to produce a pigment particle size therein in the range of from about 0.1 micron to about 1.0 micron; (c) mixing a surface active agent with the slurry of step (b) so that the pigment is coated therewith, the surface active agent being a mixture of ethoxylated sorbitan derivatives having HLB values in the range of from about 2 to about 15, non-ethoxylated mono and diglycerides having HLB values in the range of from about 2 to about 15 and ethoxylated mono and diglycerides having HLB values in the range of from about 2 to about 15; and (d) spray drying the titanium dioxide pigment coated in accordance with step (c).
The ethoxylated sorbitan derivative in the mixture of surface active agents is preferably present therein in an amount of about 70% by weight of the mixture with the non-ethoxylated mono and diglycerides and ethoxylated mono and diglycerides making up the remainder of the mixture. Also, the pigment is preferably present in the slurry formed in step (a) in an amount of about 34% by weight of the slurry, and the slurry is preferably formed at a temperature of about 25xc2x0 C. The surface active agent mixture is mixed with the slurry in accordance with step (c) in an amount of about 1% by weight of pigment in the slurry, and the surface active agent is preferably coated on the pigment in accordance with step (c) in an amount of about 1% by weight of the pigment. Also, step (c) is preferably carried out in a time period of about 5 minutes. The dried titanium dioxide pigment produced in step (d) can be micronized if desired, preferably by jet milling.
As mentioned above, if desired, the pigment can be coated with a metal oxide during step (b), and, if necessary, the pH of the slurry can be adjusted to in the range of from about 8 to about 11. Also, as mentioned above, the slurry can be filtered to increase the concentration of pigment in the slurry prior to carrying out step (c).
The dispersible pigments of this invention are particularly suitable for use in the preparation of paints and plastics concentrates. In preparing the paints and plastics concentrates, the pigment is incorporated into the paints or plastics in an amount which varies depending upon the level of pigmentation required in the final or finished end product. Generally, the paints and plastics concentrates can contain weight ratios of the pigment of this invention to the paints or plastics in which they are dispersed in the range of from about 0.5:1 to about 5:1. Within the above range, the pigment of this invention can be easily and uniformly dispersed or distributed throughout the paint or plastic.